This invention relates to a developing device for a copier having a developing tank with rollers for stirring toner therein.
In a conventional developing device for a copier, stirring rollers rotate to stir toner and its carrier together such that the toner becomes charged by friction and the rate of the roller rotation is kept constant such that the toner becomes charged to a desired constant level. When the rate at which toner is supplied into such a conventional developing device exceeds a certain level, friction between the toner and the carrier becomes insufficient to charge the toner to the desired level as shown in FIG. 8 because the rollers rotate at a fixed rate. Toner particles which are not charged sufficiently to the desired level become attached to the photoreceptor of the copier and there arises the serious problem of toner becoming transferred to areas where such toner transfer is not intended with the result that the quality of the obtained pictorial image is adversely affected.